1. Field of the Invention
The present invention relates to a double meshing-type silent chain capable of meshing with sprockets located inside and outside the chain and to a sprocket for meshing with the chain along the outer circumference thereof.
2. Description of the Related Art
Conventionally, in some cases, a double-meshing-type silent chain capable of meshing with sprockets or toothed pulleys which are mounted on respective driven shafts located inside and outside the chain is used as a timing chain for transmitting rotational motion from the crankshaft of an engine to the cam-shaft of the engine or to the shaft of an auxiliary device such as an oil pump. A double-meshing-type silent chain is employed when driven shafts located inside and outside the chain must be rotated in opposite directions.
FIG. 10 shows a conventional double-meshing-type silent chain. In FIG. 10, an endless chain A1 meshes with a sprocket A2 located inside the chain A1 as well as with a toothed pulley A3 located outside the chain A1.
In the chain A1, links, each composed of three kinds of link plates having different shapes, are connected by pins A4. Specifically, guide link plates A5 are disposed at the widthwise outermost sides of the chain A1 as well as alternately along the longitudinal direction of the chain A1. As shown in FIG. 11, the guide link plate A5 has a straight edge portion a formed at the inner circumferential side of the chain A1 and two small meshing teeth b which are formed at the outer circumferential side of the chain A1 to be located at longitudinally opposite end portions of the guide link plate 5. The small meshing teeth b mesh with the toothed pulley A3.
A link plate A6 is pin-connected with adjacent guide link plates A5 at opposite end portions thereof such that the link plate A6 is in contact with inside faces of the guide link plates A5. The link plate A6 has two meshing teeth c formed at the inner circumferential side of the chain A1 so as to mesh with the sprocket A2, as well as two small meshing teeth b formed at the outer circumferential side of the chain A1 so as to mesh with the toothed pulley A3.
Plates A7 and A8 each have two meshing teeth c formed at the inner circumferential side of the chain A1 so as to mesh with the sprocket A2, as well as a flat back face d formed opposite to the meshing teeth c.
Notably, the meshing teeth c formed at the inner circumferential side of the chain A1 and the teeth of the sprocket A2, which mesh with the meshing teeth c, employ a standard tooth profile. By contrast, the meshing teeth b formed at the outer circumferential side of the chain A1 and the teeth of the toothed pulley A3, which mesh with the meshing teeth b, employ a non-standard tooth profile.
The above conventional double-meshing-type silent chain employs three kinds of link plates having different shapes. Thus, in a step of manufacturing plates, link plate dies corresponding to the different link plate shapes must be used. Also, in an assembling step, a large number of kinds of component parts must be handled and controlled. As a result, manufacturing cost is high.
Also, since the profile of the meshing teeth formed at the outer circumferential side of the chain is smaller than the standard tooth profile, when a large load torque acts on the toothed pulley located outside the chain, the toothed pulley disengages from the chain and slips along the chain. Thus, a maximum torque that can be transmitted to the toothed pulley is smaller than that which can be transmitted to the sprocket located inside the chain. This significantly limits the selection of a device to be driven through engagement with the outer circumference side of the chain.
Further, the guide link plate has no meshing teeth at the inner circumferential side of the chain, but instead has the straight edge portion at the inner circumferential side of the chain. Consequently, the guide link plate is relatively heavy, causing an increase in the weight of the entire chain. This causes an increase in impact energy generated due to meshing engagement between the chain and the sprocket or between the chain and the toothed pulley when the chain travels, resulting in an increase in working noise.
Also, a heavy chain weight causes an increase in tension derived from a centrifugal force produced when the chain travels, accelerating wear of a shoe surface of a chain guide or the like as well as elongation of the chain. Particularly, when such a double-meshing-type silent chain is used as a timing chain for an engine, timing drive of the engine may be adversely effected.